Moistureproofed kraft paper



- Feb. '20, 1945. H. R. ms Er AL 2,370,090

Iva/slur: V400)- Wawzmswoa fife Iva/24in:

MOISTUREPROOFED KRAFT PAPER Filed Sept. 26, 1941 0 IJ W Ckramsfi arm/1' Patented Feb. 2c, 1945 ,UNITED STATES PATENT, OFFlCE 2.370.090 MOISTUBEPROOFED 1mm PAPER Herman B. Thies, Kent, and Clarence M. Carson,

Cuyahoga Falls, Ohio, assignors to Wingfoot Ohio, a corporation of Corporation, Akron,

Delaware Application Septemberitli, 1941 SerialNo. 412,408

4 Claims. (01. 111-155) I made by uniting two sheets of kraft paper with a layer of as phalt, but the number of places where such a sheet can be used is limited.

For some time there has been a water-finished kraft on the market, and this has sometimes been referred to as a calendered kraft. Even after this treatment the kraft is so absorbent that it is im- I practical to. coat it with a moistureprooflng lac- According to this invention kraft paper is super-calendered, i; e., it is passed through a high pressure, hot calender, such as, for example, a calender of the type ordinarilylemployed for glassine paper, and this super-calendered kraft is then coated with a moistureprooflng lacquer. Be-

cause such calendering tends toembrittle the paper a plasticizer such as glycerine, etc. may be added to it to keep its'moisture' content, up.'

Super-calendered kraft has-such a glaze on its surface that its power of absorbing liquids is "greatly reduced. A few pounds of of moistureproofing lacquer per ream ofpaper will render this type of kraft very resistant tothe passage of water-vapor. The paper itself is cheap. nd it can be super-calendered for not more than one cent per pound, and because it can be made'mois tureproof by a very thin coating of lacquer, a low cost moistureproof sheet is obtained which has a wide range of usefulness.

Molstureproof super-calendered kraft is im- 'mediately replacing more expensive materials and is being used where paper products'have not ping of photographic films, etc. It may be used as a linerfor barrelsand for strawboarcl cartons and for freight cars, etc. It may be used as the inner ply of multiple-ply kraft bags, such as those used for packaging salt, lime, calcium sulphate,

calcium chloride and other. hydroscopic chemicals etc. It may be used for wrapping automobile or airplane parts for export. .There are numerous possible uses forit where it is desired either to keep moisture ina packaged product or to protect a packaged product from the moisture vapor in theatmosphere.

There are various grades of kraft on the market. Any pf these may be super-calendered and lacquered to form the moisture-proof sheet 0!.

this invention. By holding a sheet of kraft paper to the light it will be observed that in certain of them the fibers are bunched together whereas in others the fibers are more uniformly distributed.

The degree of distribution of the .flbers is determined by the treatment of the pulp in the beater. A kraft in which the fibers are more evenly distributed than in ordinary kraft requires less labquer per ream to' produce any desiredmoisture resistance; and is therefore preferred in making the moisture proof sheet of this invention. the

I weight of the sheet which 'is'lacquered may vary.

. dered kraft may be used.

heretofore been employed, because no moistureproof paper of sufficient strength-was available. The combination of high strength and moisture-' proofness of the type produced by a lacquer coating has not heretofore been available in a paper product. Many uses for this new sheet have 'ala ready beenfound. For example, it may be used where metal foils are now used, as, for example,

For example. it may -be twenty or sixty pounds, more or less, per three-thousand square foot ream. Both bleached and white super-calen- A wide variety of coating materials may be used for moistureprooflng. Wax alone is unsatisfactory, because it cracks when thepaper is wrinkled or creased. Wax may be usedadvantageously wit a film-forming lacquer, such as a cellulosic prci uct, e. g nitrocellulose; or a rubber derivative, e. g., Marbon B, the product manufac tured by the Marbon Corporation of Gary, In-- dlana, which is mad by dissolving rubber-in cresol and treating e solution with hydrogen chloride as described in'McKenzie United States Patent No. 2,230,359; or a cyclized rubber such as one of the moistureprooflng Pliolite compositions sold by. The Goodyear Tire I: Rubber Company of Akron, Ohio (which may be made by treating rubber with chlorostannic acid or tin tetrachloride as described in Endres United States Patent No. 2,052,391) A chlorinated rubin the insulation of telephone cables and in wrapbar, such as Parlon, etc., or rubber hydrochloride may be used as the moistureproofing coating.- Isolac (phenol sulphonic acid derivative of rubber) may be used where its reddish color-is not objectionable. A coating of a synthetic material, such as a polyvinyl derivative may be used. Other coatings which may be used include ethyl cellulose, etc. Although the film-forming materials may be used without wax a more moistureproof product will ordinarily be obtained by compounding wax with the fllm-forming material. Fusible coatings. such as those of high wax content may be applied by the hot-melt method. The invention relates more particularly to the use of non-fusible coatings which must be applied in solution.

The following coating compositions-when applied to a super-calendered kraft in an amount (on the dry basis) of several pounds per ream, not exceeding about ten or twelve pounds per ream and in some cases not over four or five pounds per ream, will give a coated product of very low moisture transmission. The sheet is preferably coated on both sides, but may be coated on only one side. For example, three to nine pounds of the coatings of Examples 2, 3 and 4, below, one-half applied to each side of a supercalendered kraft, give a moisture transmission as low as one to six grams. The coating is preferably applied as a lacquer, and in driving off the solvent the coating in each instance should be heated to a temperature suflicient to dissolve the wax.

The accompanying graph shows the relative moistureproofness of ordinary kraft paper and super-calendered kraft to which varying amounts of a moistureproofing lacquer were applied. In treating both sheets, an equal amount of the The moisture-vapor transfer rate of ordinary kraft, uncoated, is several thousand grams per square meter in twenty-four hours. It will be noted that the lacquer coating reduces this very appreciably, but due to recentimprovements in technique a moisture-vapor transfer rate of no more than eight grams per square meter per twenty-four hours is now demanded for many uses. Thislow transfer rate cannot be obtained by coating ordinary kraft. The. cost of the amount of lacquer required makes such a pro- Cedure unprofitable, and impregnation and coatand this facilitates the formation of a skin coating .of the lacquer on thesur'face of the sheet. By retarding penetration and confining the lacquer coating to the surface of the sheet the super-calendered surface produces a skin coating from much lesslacquer than isrequired for lacquer was applied to each side of the sheet.

moisture transmission is expressed in grams per square meter per twenty-four hours.

The followingexamples are illustrative:

Example 1 Parts Cyclized'rubber (Pliolite with a distortion point of 55 C.).; l5 Parafiin, 134 F 15 Toluol 70 This formula is designed for use where anon glossy coating is desired.

Antioxidant (monobenzyl p a r a a. min 0 phenol) .72 Toluol 79.48

This coating heat-seals when heated at about 200250 F.

Example 4 Parts Partially oxidized cyclized rubber (Pliolite,

P-12'30) 18.7 Parafiin, 134 F 3.3 White petrolatum (petroleum jelly) 1.0

Toluol 77.0

This coating heat-seals at 300-400 F.

All of these formulas may be modified by using any other parafiin than those specified. Using a higher melting point parafiln there is less tendency for the treated paper to stick together in the roll.

A small amount, e. g., 0.75 part of the reaction product of tetraethylene pentamine and formaldehyde (either paraformaldehyde or Formalin) added to the composition of Example 1, 2, 3 or 4with either type of parainn gives a coating which maintains high moisture resistance over a much-longer time than the identical .Pliolite coating which contains no antioxidant or stabilizer. for the cycllzed rubber. This particular stabilizer and. related compounds such as other aldehyde and ketone derivatives of polyalkylene polyamines are not afiected by heat and therefore withstand accelerated oven-aging tests as well as giving prolonged life under normal the production of a comparable coating on ordinary ln'aft'. Equal amounts -ot'laoquer produce a much more impervious coating on the supercalendered' sheet.

The moisture-vapor herein are determined by measuring the rate of moisture. transfer between atmospheres of no humidity and one hundred per cent humidity, re-' spectively, at 40 C. for twenty four hours. The

transmissions specified f aging conditions.

A large number of other materials may be compounded with Pliolite and wax to form satise factory coatings for specific purposes. For instance, suitable coatings may be made using one to twenty-five per cent :of such resins as ester gum, cumar, polymerized terpenes, cyclohexanone, Aroclorsv and rosin esters added as diluents' or as gloss producers; and such plasticizers as, diarnylnaphthalene, tricresyl phosphate, dibutyl sebacate,.mineral oil, paraflln oil and many similar liquids may be used'ln proportions from one-to twenty per cent for specific purposes.

, Pigments, dyes, etc.-may be added to the coatings to produce desired colored eflects, although in'general colorless, transparent coatings will be preferred.

solventfthe kraft being super-calendered to con-4 The same general formulations as in Examples 1 to 4 may be used with the othermoistureproofing resins. With Marbon B or Isolac ten to fifteen per cent 'of paraflin wax may be used. Not over ten per cent of paraflin will ordinarily be used with Parlon.

Example 5- Parts Ethocel (8 cps.) I 10.0 Paraflin Castor oil 1.0 Toluol 57.5 Amy! acetate 30.0

All of these solutions may be applied on a conventional type coating machine in which the paper is passed through a tank containing the coating solution, thence over doctor knives or fine the coating to the super-calendered 8H1!- face and being plasticized to keep its moisture I content up.

2. Super-calendered kraft paper coated with a moisture-proof iacquer coating of cylized rubber, the paper being super caiendered to confine the coating to the super-calendered surface and being plasticized to keep its moisture content up..

3. A moisture-vapor-proot wrapping material consisting otesuper-caiendered kraft paper ,with

a moisture-vapor-proof lacquer skin coating thereon, the paper being super-caiendered to confine the coating to the super-calendered' surface and being piasticized to keep its moisture content up.

- 4. A moisture-vapor prooi wrapping material consisting of super-caiendered kraft paper with, Q a moistureproof lacquer skin coating of cyclized rubber thereon, the paper being'super-calendered to confine the coating to the super-calend'ered surface and being 'piasticized to keep its moisture content up.

' HERMAN R.

CLARENCE M. CARSON. 

